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61.
Edoardo Cesarotti Maria Grassi Laura Prati
Francesco Demartin
《Journal of organometallic chemistry》1989,370(1-3):407-419The DANTE technique and NOESY two-dimensional method have been employed to observe the isomerization of the chiral cationic complex [Pd(η3-CH2CMeCH2(P-P′)]+ (1a), where P-P′ = the chiral chelating ligand (S)(N-diphenylphosphino)(2-diphenylphosphinoxymethyl)pyrrolidine. The rate constant was found to be 0.5 s−1 in CHCl3 at 295 K and 1.50 s−1 in the presence of added free ligand. In the latter case the epimerization proceeds by a π-σ-π mechanism via the intermediacy of a primary η1-allylpalladium complex. Although the intermediate was not detected, the NMR findings reveal that it has the allylic terminus η1-bonded to palladium. The structure of 1a in its PF6− salt has been determined. The compound crystallizes in the orthorhombic space group P212121 with a 10.029(4) b 19.203(8) c 36.115(6) Å, Z = 8, R = 0.0572 and Rw = 0.0712 for 3716 observed reflections with I > 3σ(I). 相似文献
62.
63.
Giuseppe Bruno Francesco Nicol Archimede Rotondo Francesco Foti Francesco Risitano Giovanni Grassi 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(12):o879-o883
Conformational analyses and a structural comparison of the four spiro compounds 3‐bromo‐1,9‐diphenyl‐4‐p‐tolyl‐7‐oxa‐1,2,8‐triazaspiro[4.4]nona‐2,8‐dien‐6‐one, (I), C24H18BrN3O2, 3‐bromo‐4‐(4‐methoxyphenyl)‐1,9‐diphenyl‐7‐oxa‐1,2,8‐triazaspiro[4.4]nona‐2,8‐dien‐6‐one, (II), C24H18BrN3O3, 3‐bromo‐4‐(4‐chlorophenyl)‐1,7,9‐triphenyl‐1,2,7,8‐tetraazaspiro[4.4]nona‐2,8‐dien‐6‐one, (III), C29H20BrClN4O, and 3‐bromo‐1,7,9‐triphenyl‐4‐p‐tolyl‐1,2,7,8‐tetraazaspiro[4.4]nona‐2,8‐dien‐6‐one, (IV), C30H22.89Br1.11N4O, are presented. The molecular structures are rather similar, which is as expected since the compounds are all products of concerted 1,3‐dipolar attack on (Z)‐4‐arylidene oxazolone and pyrazolone derivatives. The observed conformations tend to favour extended π conjugation of the benzene rings and other π systems, as shown by a comparison of selected geometric parameters of the four structures. 相似文献
64.
Giuseppe Bruno Archimede Rotondo Giovanni Grassi Francesco Foti Francesco Risitano Francesco Nicol 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(7):o496-o497
The title compound, C18H15BrN2O5, a promising N‐protected α‐amino acid, was synthesized directly from an unusual bromo dipole and a 4‐(arylmethylene)oxazolone. The crystal packing of the title compound is a racemic mixture. Peculiar graph‐set motifs driven by the most important hydrogen bonds are described. 相似文献
65.
Zotkin DN Duraiswami R Grassi E Gumerov NA 《The Journal of the Acoustical Society of America》2006,120(4):2202-2215
An efficient method for head-related transfer function (HRTF) measurement is presented. By applying the acoustical principle of reciprocity, one can swap the speaker and the microphone positions in the traditional (direct) HRTF measurement setup, that is, insert a microspeaker into the subject's ear and position several microphones around the subject, enabling simultaneous HRTF acquisition at all microphone positions. The setup used for reciprocal HRTF measurement is described, and the obtained HRTFs are compared with the analytical solution for a sound-hard sphere and with KEMAR manikin HRTF obtained by the direct method. The reciprocally measured sphere HRTF agrees well with the analytical solution. The reciprocally measured and the directly measured KEMAR HRTFs are not exactly identical but agree well in spectrum shape and feature positions. To evaluate if the observed differences are significant, an auditory localization model based on work by J. C. Middlebrooks [J. Acoust. Soc. Am. 92, 2607-2624 (1992)] was used to predict where a virtual sound source synthesized with the reciprocally measured HRTF would be localized if the directly measured HRTF were used for the localization. It was found that the predicted localization direction generally lies close to the measurement direction, indicating that the HRTFs obtained via the two methods are in good agreement. 相似文献
66.
Water has been investigated for a long time as the most important solvent; the peculiar behavior of water as solute has been studied in binary mixtures with organic solvents, mainly exploring the whole phase diagram. In this Article, we studied the behavior of water in binary mixtures with propylene carbonate in the phase diagram region where water acts as a solute as a function of the water molar fraction X(water). Surface tension measurements, differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR) have been used to investigate the state of water molecules and hydrogen bonds when water is to be considered a solute instead of a solvent, and peculiar and interesting properties were discovered. The interaction of water molecules among themselves and between water and propylene carbonate has been shown to be dependent on the water concentration in the mixtures. All of the measured properties showed a break at X(water) approximately 0.15-0.20 similar to the break due to the critical micellar concentration in surfactant solutions. In particular, from the FTIR spectra, it was possible to deduce that at this concentration water has a transition from pure solute ("multimers" solvated by PC) to cosolvent ("intermediate" and "network" water). 相似文献
67.
Ambrosio M Antolini R Auriemma G Baker R Baldini A Bam B Barbarino GC Barish BC Battistoni G Bellotti R Bemporad C Bernardini P Bilokon H Bisi V Bloise C Bower C Bussino S Cafagna F Calicchio M Campana D Carboni M Corona A Cecchini S Cei F Chiarella V Cormack R Coutu S DeCataldo G Dekhissi H DeMarzo C De Vincenzi M Di Credico A Diehl E Erriquez O Favuzzi C Forti C Fusco P Giacomelli G Giannini G Giglietto N Grassi M Green P Grillo A Guarino F Guarnaccia P Gustavino C Habig A Heinz R Hong JT 《Physical review D: Particles and fields》1994,50(5):3046-3058
68.
69.
The ligand exchange rate constants for the reactions [Pt(bph)(SR2)2] + 2*SR2 --> [Pt(bph)(*SR2)2] + 2SR2 (bph = 2,2'-biphenyl dianion; R = Me and Et) and cis-[PtPh2(SMe2)2] + 2*SMe2 --> cis-[PtPh2(*SMe2)2] + 2SMe2 have been determined in CDCl3 as a function of ligand concentration and temperature, by 1H NMR isotopic labeling and magnetization transfer experiments. The rates of exchange show no dependence on ligand concentration and the kinetics are characterized by largely positive entropies of activation. The kinetics of displacement of the thioethers from [Pt(bph)(SR2)2] with the dinitrogen ligands 2,2'-bipyridine and 1,10-phenanthroline (N-N) to yield [Pt(bph)(N-N)], carried out in the presence of sufficient excess of thioether and N-N to ensure pseudo-first-order conditions, follow a nonlinear rate law k(obsd) = a[N-N]/(b[SR2] + [N-N]). The general pattern of behavior indicates that the rate-determining step for substitution is the dissociation of a thioether ligand and the formation of a three-coordinated [Pt(bph)(SR2)] intermediate. The value of the parameter a, which measures the rate of ligand dissociation, is constant and independent of the nature of N-N, and it is in reasonable agreement with the value of the rate of ligand exchange at the same temperature. Theoretical ab initio calculations were performed for both [Pt(bph)(SMe2)2] and cis-[PtPh2(SMe2)2], and for their three-coordinated derivatives upon the loss of one SMe2 ligand. The latter optimize in a T-shaped structure. Calculations were performed in the HF approximation (LANL2DZ basis set) and refined by introducing the correlation terms (Becke3LYP model). The activation enthalpies from the optimized vacuum-phase geometries are 52.3 and 72.2 kJ moll compared to the experimental values in CDCl3 solution, 80 +/- 1 and 93 +/- 1 kJ mol(-1) for [Pt(bph)(SMe2)2] and cis-[PtPh2(SMe2)2], respectively. The electrostatic potential maps of both parent compounds show a remarkable concentration of negative charge over the platinum atom which exerts a repulsion force on an axially incoming nucleophile. On the other hand, the strength of the organic carbanions trans to the leaving group and the stabilization of the T-shaped intermediate in the singlet ground state may also rationalize the preference for the dissociative mechanism. All of the kinetic and theoretical data support the latter hypothesis and indicate, in particular, that dissociation from the complex containing the planar 2,2'-biphenyl dianion is easier than from its analogue with single aryl ligands. Electron back-donation from filled d orbitals of the metal to empty pi* of the in-plane cyclometalated rings is weak or absent and is not operative in promoting an associative mode of activation. 相似文献
70.
Francesco Foti Giovanni Grassi Francesco Risitano Salvatore La Rosa 《Journal of heterocyclic chemistry》2001,38(2):539-540
The synthesis of a series of 3‐Imidazolylazole derivatives using cycloaddition reactions of a useful new nitrile oxide is described. 相似文献